Reported by ACI Committee E 706

J. Christopher Ball* Bob Joyce Kelly M. Page

Peter H. Emmons† Brian F. Keane Jay H. Paul

Timothy R. W. Gillespie Kenneth M. Lozen George I. Taylor

H. Peter Golter John S. Lund Patrick M. Watson§

Fred R. Goodwin

RAP-9

Spall Repair by thePreplaced Aggregate Method

David W. Whitmore‡

Chair

*Primary author of RAP Bulletin No. 6.†Primary author of RAP Bulletin No. 7.‡Primary author of RAP Bulletin No. 8.§Primary author of RAP Bulletin No. 9.

The committee would like to thank Brandon Emmons for his illustrations in these bulletins.

ACI Repair Application Procedure 9.Copyright © 2005, American Concrete Institute.All rights reserved including rights of reproduction and use in any

form or by any means, including the making of copies by any photo pro-cess, or by electronic or mechanical device, printed, written, or oral, orrecording for sound or visual reproduction or for use in any knowledgeretrieval system or device, unless permission in writing is obtained fromthe copyright proprietors. Printed in the United States of America.

The Institute is not responsible for the statements oropinions in its publications. Institute publications arenot able nor intended to supplant individual training,responsibility or judgment of the user, or the supplier ofthe information provided.

Structural DisclaimerThis document is intended as a voluntary field guide forthe Owner, design professional, and concrete repair con-tractor. It is not intended to relieve the user of this guideof responsibility for a proper condition assessment andstructural evaluation of existing conditions, and for thespecification of concrete repair methods, materials, orpractices by an experienced engineer/designer.

It is the responsibility of the user of this document toestablish health and safety practices appropriate to the specificcircumstances involved with its use. ACI does not make anyrepresentations with regard to health and safety issues and the useof this document. The user must determine the applicability ofall regulatory limitations before applying the document andmust comply with all applicable laws and regulations,including but not limited to, United States OccupationalSafety and Health Administration (OSHA) health andsafety standards.

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Spall Repair by the Preplaced Aggregate Method (ACI RAP-9) 1

ACI RAP Bulletin 9

Spall Repair by the Preplaced Aggregate Method

FIELD GUIDE TOCONCRETE REPAIR

APPLICATION PROCEDURES

by Patrick “Doc” Watson

2 Repair Application Procedures Bulletin

IntroductionPreplaced-aggregate concrete (PPA) is defined as

“Concrete produced by placing coarse aggregate in a formand later injecting portland cement-sand grout, usually withadmixtures, to fill the voids.” ACI 304.1R-92, “Guide for theUse of Preplaced Aggregate Concrete,” provides informa-tion for job-site mixing of grout for PPA. There are alsoproprietary products available for grouting preplaced-aggre-gate concrete. Today, most preplaced-aggregate concrete isproduced with prepackaged grouts made specifically for usewith PPA.

Placing the aggregate first has several benefits:• Point-to-point contact of large aggregate is optimized;• Uniform aggregate distribution and density are achieved;• The ratio of aggregate-to-cement paste is higher than in

placeable concrete;• Aggregate can be placed in hard-to-get-at locations

such as around closely spaced reinforcing steel; and• Shrinkage is reduced by 50 to 100% compared to typi-

cal cast-in-place concrete.Before any concrete repair is carried out, assess the root cause

of the damage so the objective of the repair is understood.Typical causes of concrete damage include steel corrosion,

sulfate attack, freezing-and-thawing damage, and alkali-aggregate reactions (AARs). Excessive shrinkage of theoriginal concrete and/or settlement in the structure may be acause of damage. Improper joint spacing and load imbal-ances also contribute to cracking and spalling.

What is the purpose of this repair?Preplaced-aggregate concrete is used for repairs to restore

structural integrity, provide extra cover, reduce the potentialfor shrinkage-related repair failures, and for underwaterrepair, particularly when cofferdams are impractical.

When do I use this method?Preplaced-aggregate concrete is most often used for

vertical, overhead, and underwater repairs. It can be used forhorizontal repairs. PPA is often chosen when repairs requiregetting concrete into tight or hard-to-reach areas. The appli-cations can be structural or cosmetic. Successful applicationshave included dam faces, spillways, bullnoses, and bridgecolumns and footings. Many of these applications haverequired that repairs be completed under water and some-times in moving water.

This method has been particularly successful for jacketingcolumns.

The preplaced aggregate method can be used for mostrepair applications that call for a thickness or depth greaterthan 2 in. (50 mm). An experienced contractor workingunder the guidance of a qualified engineer is the best choicefor repairs using this method.

Forming is very similar to that used for cast-in-placeconcrete. The forms must be watertight. The selection andpreparation of materials also require careful attention todetail (see the “Repair procedure” and “How do I select thecorrect materials?” sections).

This method of repair can have higher labor costs thancast-in-place concrete but has proven to be effective whereshrinkage of the repair cannot be allowed.

How do I prepare the surface?Consult the recommendations of International Concrete

Repair Institute (ICRI) Guideline No. 03732, “Selecting andSpecifying Concrete Surface Preparation for Sealers, Coat-ings, and Polymer Overlays,” or No. 03730, “Guide toSurface Preparation for Repair of Deteriorated ConcreteResulting from Reinforcing Steel Corrosion.” Also, consultthe manufacturer of any prepackaged grout to be used.

Factors that will influence surface preparation for thespecific application include, but are not limited to:• Desired roughness profile of the prepared surface;• The method of preparation, such as: hydrodemolition,

sandblasting, use of pneumatic hammers, and shot-blasting;

• Possible contamination of the surface by oils or soaps, orsurface carbonation—both of which require additionalpreparatory steps. These may include pressure washing,hot-water pressure washing, cleaning with degreasingdetergents, and chemical extraction methods;

• Requirements for saturation of concrete in the area tobe repaired;

• Reinforcing requirements by the engineer or owner;• Treatment of existing cracks and joints in the substrate;

and• Repair the cracks? How? Fill the joints? If so, how and

with what?Surface preparation is similar to that for most concrete

repairs. With the above considerations in mind, concrete isremoved until acceptable-quality concrete is located andrevealed. Reinforcing steel, if exposed, is undercut, and allexposed surfaces are cleaned with high-pressure water(minimum 3000 psi) or are abrasively blasted. With PPArepairs, consideration should be given to how the grout willbe pumped into the forms and through the aggregate from thebottom up (refer to ACI 304.1R).

How do I select the right materials?Use sound, tested, properly graded aggregate. Test aggre-

gate for reactivity in accordance with ASTM C 1260. Gradethe aggregate in accordance with the recommendations ofTable 1 of ACI 304.1R. Rewash the aggregate.

Considerations in grout selection include:• The traditional material used for PPA grout has been

site-mixed sand-cement with the addition of grout flu-idifiers and aluminum powder. These materials can bedifficult to control and keep consistent under field con-

Fig. 1—Preparation

Spall Repair by the Preplaced Aggregate Method (ACI RAP-9) 3

ditions. Control of expansion and bleeding are very dif-ficult. Prepackaged products made specifically for usein preplaced-aggregate concrete should provide greaterconsistency and control;

• Grouts with pretested freezing-and-thawing resistanceshould be used where repairs will be exposed to freez-ing-and-thawing cycles;

• Grouts with corrosion-inhibiting admixtures should beconsidered where corrosion of reinforcing steel is a factor;

• Very low or no bleeding of the fluid grout is necessaryto ensure quality repair with PPA; Bond characteristicsfor grout should be tested in accordance with ACI 503RAppendix A; see ICRI Technical Guideline 03739,“Guide to Using In-Situ Tensile Pull-Off Test to Evalu-ate Bond of Concrete Surface Materials.”

• Test compressive strength of grouts in accordance withASTM C 942;

• Make all tests on grout mixed to flow consistency to beused in repair; and

• Test compressive strength of the grout and aggregatecombination in accordance with ASTM C 943. This is aspecial method of testing. Be sure to consult with thetesting laboratory and engineer to ensure that propertest equipment is on-site and technicians are trained inthe procedure.

What equipment do I need?• Test equipment, if not provided by an independent labo-

ratory: Flow cone in accordance with ASTM C 939 andPPA test cylinders in accordance with ASTM C 943;

• Placement equipment: Water meter or water measuringdevice;

• pH indicator such as phenolphthalein;• Concrete or grout pump (not ball valve type): Short-

stroke, swing-type piston pumps or heavy-duty rotor-stator pumps perform well. If using a rotor-stator or“moyno”-type pump, have a backup rotor on hand atthe job site;

• Grout mixers, if not built into pump: Use tub-type verticalshaft mixers or horizontal shaft mortar mixers with rubberblade wipers. (Do not use portable concrete mixers with arotary drum.) Have a backup mixer available in case ofbreakdown. Some specialty concrete/grout pumpscome equipped with mixers and water meters;

• For large projects, grout can be batched into ready-mixconcrete transit mixer trucks, or prepackaged grout isavailable in bulk bags up to 3300 lb (1500 kg) each;

• A sieve of adequate size for on-site grading of aggre-gate if a pre-graded supply is not available;

• A method of rewashing sieved-graded aggregate. Thismay be a second sieve with washout hoses and agitator;

• Connector valves or shutoffs for grout inlet pipes; and• A sprayer, rollers, or brushes if a curing compound is

required.

What are the safety considerations?Safety considerations include but are not limited to:Portland cement-based materials are alkaline and abrasive,

and should be treated as such. Job-site safety practicesshould include:• Having Material Safety Data Sheets for products on site

and reviewing them before startup;• Having correct safety guards, maintenance, and warn-

ings in place for all machinery and equipment to beused;

• Having all workers wearing protective eyewear, safetyglasses, or face shields;

• Having all workers in contact with wet cementitiousmaterial wearing protective gloves (rubber- or neo-prene-coated) and clothing;

• Having eyewash facilities available on site;• Providing dust masks for workers operating material

mixers;• Confirming that adequate ventilation is available in

closed spaces before operating equipment or usingproducts that emit dangerous exhaust, fumes, or dust;

• Having secured storage available for all hazardous orflammable materials; and

• Holding a safety meeting for all involved parties, leadby the prime contractor’s safety manager, prior tobeginning repair operations.

It is the responsibility of the user of this document toestablish health and safety practices appropriate to thespecific circumstances involved with its use. ACI does notmake any representations with regard to health and safetyissues and the use of this document. The user must determinethe applicability of all regulatory limitations before applyingthe document and must comply with all applicable laws andregulations, including but not limited to, United States Occu-pational Safety and Health Administration (OSHA) healthand safety standards.

Preconstruction meetingPrior to proceeding with the repair, a preconstruction

meeting is recommended. The meeting should include repre-sentatives from all participating parties (owner, engineer,contractor, materials manufacturer, etc.), and specificallyaddress the parameters, means, methods, and materialsnecessary to achieve the repair objectives.

Include the owner’s representative, the specifier, theproject manager, the repair grout manufacturer, and theconstruction team foreman. See ICRI Guideline No. 03733,“Guide to Selecting and Specifying Materials for Repair ofConcrete Surfaces,” for additional agenda items.

The preconstruction meeting list or agenda might include:• On-site availability of power;• On-site availability of mixing water;• Site accessibility;• Debris removal and disposal;• Dust, odor, and emissions control;• Control of water runoff;• Confirmation that all materials and equipment are

available. Pay particular attention to required quantitiesof grout and graded, washed aggregate;

• Confirmation that all material documentation is on site;for example, MSDS information;

• Noise control;• Methods of curing and time required for curing;• Responsibility for quality control and final acceptance;• Possible emergencies and breakdowns—what to do if

they occur; and• All other concerns that could affect the progress of the

repair.

4 Repair Application Procedures Bulletin

Repair procedure1. Install the repair.A. Inspect and approve the surface preparation.Check surface for contamination.B. Saturate the prepared surface if required.C. Set forms grout-tight.Commonly used grout-head pressure number is 10 psi

(70 kPa).When form joints do not match perfectly, seal them

from the inside with adhesive tape.Where forms fit against original concrete, seal with thick

mortar, strong compressible material, or caulking rope.Avoid the use of caulks as they may yield under head pres-sure from the grout.

D. Grade the aggregate.PPA requires gap-graded aggregate. This can be provided

as specified in ACI 304.1R, by a supplier, or sieved on site.E. Saturate the aggregateSaturate the aggregate to prevent rapid absorption of water

from the grout and thickening of the grout as it flows.F. Place clean/saturated aggregate as the forms are

erected.Do not drop aggregate more than 5 ft (1.5 m) except where

repairs are under water and aggregate will fall through water.Place grout pipes and observation tubes if required (see

ACI 304.1R for suggestions concerning placement of groutpipes and observation tubes).

Inlet pipe placement will vary depending on the repairconfiguration.

G. Batch the grout.Typical mixing equipment for mixing grout is a two-tub

mixer equipped with a rotor-stator pump and a water meter.These pumps are commercially available from several groutpump manufacturers. Do not use ball-valve pumps.

Have adequate mixing and pumping equipment on hand.This usually means at least one backup unit.

If using prepackaged grout, consult the manufacturer formixing recommendations.

Check the grout consistency. Grout should be tested inaccordance with ASTM C 939. This is the flow cone test forconsistency. A flow of 10 to 30 s is typical for site-madegrouts; prepackaged grouts should have flow values asrecommended by the manufacturer.

H. Pump and place the grout.Provide a means of communication between mixer/ pump

operator and placement crew.Connect pump hose to grout inlet openings or pipes.Start placement at bottom of aggregate placement.External form vibration will aid in grout consolidation. It

is not always necessary with well-graded aggregates andgood quality grout.

When forms appear full, keep light pressure on from pumpfor several minutes to prevent sagging and displace water/airfrom forms. Stop if grout is spilling out of forms.

2. Finish the repair.Confirm what the final finished appearance of the repair is

to be at the open areas of the forms.If vertical formed repairs with open tops are used, work

small aggregate (3/8 or 3/4 in. [10 or 20 mm]) into thesurface. Finish as required.

Cure PPA in the same manner as conventional concrete,per ACI 308.

How do I check the repair?Typical procedures could include:

• Document the project before, during, and after withphotos;

• Pre-confirm the acceptability of the prepared surface,including any pH requirements, and the specified sur-face profile;

• Have all materials pre-tested by a qualified test laboratoryfor compliance with manufacturers’ stated properties;

• Perform in-place tensile pulloff tests of the preparedsubstrate surface; Confirm the quality of bond of the

Fig. 2—Forming

Fig. 3—Aggregate placement

Fig. 4—Pumping grout

Spall Repair by the Preplaced Aggregate Method (ACI RAP-9) 5

completed repair by direct tensile bond test (ACI 503RAppendix A, see “ICRI Technical Guideline 03739,Guide to Using In-Situ Tensile Pull-Off Test to Evalu-ate Bond of Concrete Surface Materials.”); and

• Confirm that all materials used were as specified, crosscheck material purchase orders with quantities estimatedand with actual quantities billed.

Sources for additional informationACI Committee 304, 1992, “Guide for the Use of Preplaced Aggregate

Concrete for Structural and Mass Concrete Applications (ACI 304.1R-92),” American Concrete Institute, Farmington Hills, Mich., 19 pp.

ACI Committee 308, 2001, “Guide to Curing Concrete (ACI 308R-01),”American Concrete Institute, Farmington Hills, Mich., 31 pp.

ACI Committee 503, 1993, “Use of Epoxy Compounds with Concrete(ACI 503R-93),” American Concrete Institute, Farmington Hills, Mich.,Appendix A.

ACI Committee 546, 2004, “Concrete Repair Guide (ACI 546R-04),”American Concrete Institute, Farmington Hills, Mich., 53 pp.

ASTM C 939, 2002, “Standard Test Method for Flow of Grout for Preplaced

Aggregate Concrete,” ASTM International, West Conshohocken, Pa., 3 pp.ASTM C 942, 1999, “Standard Test Method for the Compressive

Strength of Grouts for Preplaced-Aggregate Concrete in the Laboratory,”ASTM International, West Conshohocken, Pa., 2 pp.

ASTM C 943, 2002, “Standard Practice for Making Test Cylinders andPrisms for Determining Strength and Density of Preplaced-Aggregate Con-crete in the Laboratory,” ASTM International, West Conshohocken, Pa., 4 pp.

ASTM C 1260, 2001“Standard test Method for Potential Alkali Reactiv-ity of Aggregates (Mortar-Bar Method),” ASTM International, West Con-shohocken, Pa., 5 pp.

ICRI Guideline No. 03732, “Selecting and Specifying Concrete SurfacePreparation for Sealers, Coatings, and Membranes,” International ConcreteRepair Institute.

ICRI Guideline No. 03730, “Guide to Surface Preparation for the Repairof Deteriorated Concrete Resulting from Reinforcing Steel Corrosion,”International Concrete Repair Institute.

ICRI Technical Guideline 03739, Guide to Using In-Situ Tensile Pull-Off Test to Evaluate Bond of concrete Surface Materials.

King, J., and Bush, E., 1960, “Grouting of Granular Materials,” ASCEConvention.

King, J., and Wilson, A., 1988, “If It’s Still Standing, It Can BeRepaired,” Concrete Construction, July.